1. Field of the Invention
The present invention generally relates to an effluent abatement system for the treatment of gas streams from processes such as manufacturing of semiconductor materials, devices and products. The invention relates more specifically to abatement of halogens such as fluorine and fluorinated chemical species, by reaction thereof with water vapor during thermal oxidation treatment of a halogen-containing effluent gas.
2. Description of the Related Art
Gaseous effluents from the manufacture of semiconductor materials, devices, products and memory articles may contain a wide variety of chemical species from the process facility. These chemical species include inorganic and organic compounds, breakdown products of photo-resist and other reagents, and a wide variety of other gases that must be removed from the waste gas streams before being vented from the process facility into the atmosphere.
The effluent gas in such instances may be subjected to any of a wide variety of treatments to abate the various undesirable components of the gas. Such effluent gas treatment may for example include scrubbing of the effluent gas to remove acid gas components and/or particulates from the gas stream. The gas may also be thermally oxidized to remove organic components and other oxidizable components, by mixing the effluent with an oxidant, such as high purity oxygen, air or nitrous oxide, and flowing the resulting gas mixture through a thermal oxidation reaction chamber.
In such effluent treatment systems, halogens, e.g., fluorine (F2) and fluorinated compounds are particularly problematic among the various components requiring abatement. The electronics industry uses perfluorinated compounds (PFCs) in wafer processing tools to remove residue from deposition steps and to etch thin films. PFCs are recognized to be strong contributors to global warming and the electronics industry is working to reduce the emissions of these gases.
The most commonly used PFCs include CF4, C2F6, SF6, C3F8, and NF3. These PFCs are dissociated in a plasma to generate highly reactive F2 and fluorine radicals, which do the actual cleaning, and etching. The products from these processing operations include mostly fluorine, silicon tetrafluoride (SiF4), and to a lesser extent hydrogen fluoride (HF) and carbonyl fluoride (COF2). The toxic nature of these gases poses considerable health and environmental hazards, in addition to being highly corrosive to exhaust systems.
Optimization of the operating conditions in the semiconductor manufacturing process tool to increase the conversion efficiencies (of PFCs to end products) has been the primary focus in reducing PFC emissions. An example of this approach is the Applied Materials HDP-CVD process. The improvements that have been made in PFC conversions by process optimization has enabled the use of shorter clean cycles to be achieved, and consequently higher wafer throughputs to be obtained.
The current trend in the semiconductor manufacturing industry to 300mm wafer manufacturing will increase the amounts of PFCs used in semiconductor manufacturing facilities. The increase in usage of PFCs and their conversion to highly reactive products have led to an increase in the corrosion rate of the abatement equipment and associated exhaust ductwork. In particular the corrosion attributable to fluorine has necessitated more frequent replacement of equipment components upstream of the typically employed wet scrubber unit in the effluent treatment system.
A number of reagents have been used for reaction with PFCs to convert them to compounds that are less corrosive, can easily be scrubbed from the exhaust stream, or pose less of a danger to health and the environment. For example, hydrogen (H2) can be introduced as a reagent to convert the fluorine to HF, which can then be removed using a wet scrubber. Hydrogen, however, poses a potential problem due to its explosive nature, and hydrogen has been banned from some semiconductor processing operations because of this danger.
As a result of the explosive hazard associated with H2, other reagents can be dissociated to provide hydrogen to abate the F2. Methane (CH4) can be employed to abate fluorine and fluorinated species by combustion thereof using added air or oxygen (O2). The water vapor and reactive hydrogen produced from this combustion react with the F2 and fluorinated species to convert them to HF and SiO2, which can then be readily removed from the exhaust stream.
Methane is not as explosive as H2, but suffers from other problems. The combustion of CH4 at high temperatures in the presence of oxygen produces oxides of nitrogen (NOx). Under combustion conditions where insufficient oxygen is present, the CH4 can be converted to fluorine substituted methanes (of the formula CHxFy, wherein x and y may range from 0 to 4). These fluoromethanes are of concern because of their strong global warming potential.
Both anhydrous ammonia (NH3) and aqueous ammonia (NH4OH) can also be used as reagents for F2 abatement. Ammonia increases the cost of ownership for the effluent treatment system in which it is used, and thus has a corresponding economic disadvantage. Further, the presence of ammonia can be a factor in the generation of oxygen difluoride if pH is not rigorously controlled in the effluent treatment system.
It would therefore be an advance in the art to provide a method of abatement of fluorine and other halogen species, which overcomes the various above-described deficiencies of the prior art.
The present invention relates to the abatement of halogen in a halogen-containing effluent gas stream.
In one aspect, the invention relates to an apparatus for treating the effluent fluid stream from one or more semiconductor manufacturing process tools, comprising:
an oxidizing unit having one or more inlet units at one end, downstream from at least one semiconductor manufacturing process tool, arranged to elevate the temperature of the effluent fluid stream, effect oxidation of at least a portion of the oxidizable components of the effluent fluid stream, and utilize water vapor to effect conversion of at least a portion of the halogen-containing components of the effluent fluid stream at the inlet end.
Such apparatus may in one embodiment further include a post-treatment unit, downstream from the oxidizing unit, arranged to remove acidic components from the effluent fluid stream.
Another aspect of the invention relates to a thermal oxidation reactor for abatement of oxidizable halogen components in an effluent gas, such thermal oxidation reactor comprising: a housing defining a flow passage therein for flow of effluent gas therethrough; an inlet coupled to the housing for introduction of effluent gas to the central flow passage, such inlet comprising (1) a shrouding gas flow passage arranged to flow shrouding gas into the central flow passage cocurrently with the effluent gas and surrounding the effluent gas, and (2) a reagent gas flow passage arranged to flow a reagent gas into the central flow passage cocurrently with the shrouding gas and surrounding the shrouding gas, wherein the reagent gas is reactive with halogen species in the effluent gas, with the central flow passage being of sufficient length downstream of the inlet to permit the reagent gas to mix and react with the halogen species of the effluent gas.
In one method aspect, the invention relates to a method for treating the effluent fluid stream from one or more semiconductor manufacturing process tools using a system that includes an oxidizing unit having one or more inlet units at one end, comprising the steps of:
providing water vapor to the inlet end of the oxidizing unit;
effecting, at the inlet end of the oxidizing unit, the conversion of at least a portion of the halogen-containing components of the effluent fluid stream to a form that is more treatable using such water vapor; and
effecting, in the oxidizing unit, the oxidation of at least a portion of the oxidizable components of the effluent fluid stream.
The above-described method may further comprise in a particular embodiment the additional step of removing acidic components from the effluent fluid stream.
Another aspect of the invention relates to a method of thermally oxidizing a halogen-containing effluent gas in a thermal oxidation reactor including a gas flow path bounded by a liner susceptible to corrosion in exposure to halogen species in the halogen-containing effluent gas, such method comprising introducing the halogen-containing effluent gas into the thermal oxidation reactor and flowing water vapor between the introduced halogen-containing effluent gas and the liner to thereby protect the liner by reaction of the water vapor with the halogen species in the halogen-containing effluent gas.
Other aspects, features and embodiments will be fully apparent from the ensuing disclosure.